The present invention is directed to conductive polymer materials, the method of making polymeric material and applications utilizing conductive polymer materials.
Electrically conducting polymers have been used in a variety of organic electronic devices, including in the development of electroluminescent (EL) devices for use in light emissive displays. With respect to EL devices, such as organic light emitting diodes (OLEDs) containing conducting polymers, such devices generally have the following configuration:                anode/hole injection layer/EL layer/cathode        
The anode is typically any material that has the ability to inject holes into the otherwise filled π-band of the semiconducting material used in the EL layer, such as, for example, indium/tin oxide (ITO). The anode is optionally supported on a glass or plastic substrate. The EL layer is typically semiconducting, conjugated organic material, including a conjugated semiconducting polymer such as poly(paraphenylenevinylene), polyfluorene, spiropolyfluorene or other EL polymer material, a small molecule fluorescent dye such as 8-hydroxquinoline aluminum (Alq3), a small molecule phosphorescent dye such as fac tris(2-phenylpyridine) Iridium (III), a dendrimer, a conjugated polymer grafted with phosphorescent dye, a blend that contains the above-mentioned materials, and combinations. The EL layer can also be inorganic quantum dots or blends of semiconducting organic material with inorganic quantum dots. The cathode is typically any material (such as, e.g., Ca or Ba) that has the ability to inject electrons into the otherwise empty π*-band of the semiconducting organic material in the EL layer.
The hole injection layer (HIL) is typically a conducting polymer and facilitates the injection of holes from the anode into the semiconducting organic material in the EL layer. The hole injection layer can also be called a hole transport layer, hole injection/transport layer, or anode buffer layer, or may be characterized as part of a bilayer anode. Typical conducting polymers employed as hole injection layer include polyaniline and polydioxythiophenes such as poly(3,4-ethylenedioxythiophene) (PEDOT). These materials can be prepared by polymerizing aniline or dioxythiophene monomers in aqueous solution in the presence of a water soluble polymeric acid, such as poly(styrenesulfonic acid) (PSSA), as described in, for example, U.S. Pat. No. 5,300,575 entitled “Polythiophene dispersions, their production and their use”; hereby incorporated by reference in its entirety. A well known PEDOT/PSSA material is Baytron®-P, commercially available from H. C. Starck, GmbH (Leverkusen, Germany).
Electrically conducting polymers have also been used in photovoltaic devices, which convert radiation energy into electrical energy. Such devices generally have the following configuration:
positive electrode/hole extraction layer/light harvesting layer(s)/negative electrode
The positive electrode and negative electrode can be selected from materials used for the anode and cathode of EL devices mentioned above. The hole extraction layer is typically a conducting polymer that facilitates the extraction of holes from the light harvesting layers for collection at the positive electrode. The light harvesting layer or layers typically consists of organic or inorganic semiconductors that can absorb light radiation and generate separated charges at an interface.
Electrically conducting polymers also have utility as electrodes for electronic devices, such as thin film field effect transistors. In such transistors, an organic semiconducting film is present between source and drain electrodes. To be useful for the electrode application, the conducting polymers and the liquids for dispersing or dissolving the conducting polymers have to be compatible with the semiconducting polymers and the solvents for the semiconducting polymers to avoid re-dissolution of either conducting polymers or semiconducting polymers. The electrical conductivity of the electrodes fabricated from the conducting polymers should be greater than 10 S/cm (where S is a reciprocal ohm). However, the electrically conducting polythiophenes made with a polymeric acid typically provide conductivity in the range of about 10−3 S/cm or lower. In order to enhance conductivity, conductive additives may be added to the polymer. However, the presence of such additives can deleteriously affect the processability of the electrically conducting polythiophene.
Attempts have been made to improve the properties of conductive polymer films. For example, U.S. Pat. No. 7,250,461 B2, which is hereby incorporated by reference in its entirety, discloses the addition of organic solvent in conductive polymers made with fluorinated polymeric acid colloids in order to increase the film conductivities. However, the solvents used in this disclosure fail to improve the surface tension of the formulated dispersion, leading to poor wetting property during deposition on substrate.
In addition, WO 2006/123167A1 (the WO 167 disclosure), which is hereby incorporated by reference in its entirety, discloses an ink jet ink formulation with poly(3,4-ethylenedioxythiophene)/polystyrene sulfonic acid (PEDOT/PSSA) dispersion where polyols were used as humectant together with small amount of glycol ether as surfactant. A drawback of the formulation of the WO 167 disclosure is that the use of colloid-forming dispersant PSSA, which is not at least a partially fluorinated dispersant, the conductive polymer layer formed on the substrate undesirably can adsorb moisture from the environment. This may lead to layer delamination and ultimately poor device life time.
Earlier study by Jiang et al (SPIE 2006 proceeding) titled “Enhanced Lifetime of Polymer Light-Emitting Diodes Using Poly(thieno[3,4-b]thiophene) base Conductive Polymers” concluded that conducting polymer with the colloid-forming polymeric acid comprises a highly-fluorinated sulfonic acid polymer (“FSA polymer”) has better thermal stability and low moisture residue as compared to conducting polymer with the water soluble colloid-forming polymeric acid such as poly(styrene sulfonic acid) (PSSA). This may well be one of the key factors leading to longer device lifetime, especially under high temperature and high humidity conditions.
However, conductive polymer dispersion comprising the highly-fluorinated sulfonic acid polymer as dispersing polymer alone, such as NAFION®, introduces the following two major processing deficiencies: a) hydrophobic nature of the dispersion causes poor wetting on substrate (e.g. ITO/glass, ITO/PET) and often poor adhesion to adjacent layer such as LEP layer. b) The highly-fluorinated sulfonic acid polymer is dispersible in water with limited solubility in water. As a result, the polymer dispersion utilizing only a highly-fluorinated sulfonic acid polymer has relatively low bulk viscosity. This limits the processing operating choices during the film deposition step.
What is needed is a conductive polymer and device formed from conductive polymers that are easily processed, produces high quality conductive films suitable for use in electronic components, and do not suffer from the drawbacks of the prior art.
The previously identified patents and patent applications are hereby incorporated by reference.